The other mouse could have stressed her out since she refused for a month and a half. Maybe it could have been too much of a hassle and she just wasn't ready for another.

Maybe one of the rodents bit her or scratched her and that caused her to get freaked out or stressed out.

Also, as for the ambient/cool side temp, I'd raise that to the low 80s (the ambient/cool side temp shouldn't have triggered the regurg though).